In general, as shown in FIG. 1, a battery module 1 includes: a shell 2 having a predetermined housing space that is open at the top and the bottom thereof; a battery assembly 6 having a plurality of cylindrical batteries 3 disposed in such a manner that axis lines of the batteries are parallel to each other, and battery retaining boards 5 disposed at the top and the bottom of the whole batteries 3 so as to fix the batteries 3 integrally by means of support bars 4; a lower cap 7 for fixing the lower battery retaining board 5 of the battery assembly 6 by means of the lower edge of the shell when the battery assembly 6 is inserted into the housing space of the shell 2; and an upper cap 8 for fixing the upper battery retaining board 5 of the battery assembly 6 by means of the upper edge of the shell 2.
Particularly, each of the lower cap 7 and the upper cap 8 is provided with airflow ports 9 in order to discharge heat generated from each battery 3 in the battery assembly 6 to the exterior. Additionally, the upper cap 8 is provided with terminals 8a at one side thereof so as to supply electric current to an external instrument.
However, such a conventional battery module has a problem in that batteries forming a battery assembly have a cylindrical shape and relatively large length and thus the whole volume of the battery module undesirably becomes large.
Further, because the battery assembly is large, it is not handy to laminate and integrally fix a plurality of battery assemblies in order to manufacture a battery module conformed to the electric power requirement for a desired instrument.
In another aspect, such a conventional battery module has a complicated structure because electrodes of each battery in a battery assembly are connected via connectors on the battery retaining boards. Moreover, connecting electrodes of each battery via connectors on the battery retaining boards is very cumbersome work.
Additionally, when multiple battery modules are laminated so as to be applied as a power source for an instrument requiring high output (for example a motor-drivable car), there is a great possibility of batteries being overheated while the battery modules are operated for a long time, because batteries in a battery assembly forming a battery module are in close contact with each other and surrounded with a shell.